1. Field the Invention
The present invention relates to a paper supplying device provided in an image forming apparatus, a printer and the like.
2. Description of the Prior Art
In a conventional paper supplying device provided in, for example, an image forming apparatus, a variable resistor 52 changing a resistance value in an interlocked relation with a paper width setting mechanism on a side of a paper supplying deck 50 is connected between a constant voltage power source 53 of, for example, 5V and a ground 54 and is connected with one pin 56c of a member 55a on such side of the deck where a sliding tap 52a of variable resistor 52 constitutes a drawer-type connector 55, as shown in FIG. 10. On the other hand, one pin 57c, corresponding to a pin 56c, of a body side member 55b of drawer-type connector 55 is connected with an input port of a controller (not shown) on a side of a body 51. With this construction, the resistance value of the variable resistor 52, in short a resistance from sliding tap 52a to ground 54, is converted into a voltage to be input to the controller through the connector 55 as a datum of a paper width set by means of the paper setting mechanism, whereby a width of a paper carried on a paper carrying portion of the paper supplying deck 50 is confirmed on a side of body 51 under the condition that the paper supplying deck 50 is mounted on a paper supplying portion of the body 51. That is, the deck-side member 55a of the drawer-type connector 55 is connected with body-side member 55b.
In addition, one pin 57a of the body-side member 55b constituting the drawer-type connector 55 is connected with a constant voltage power source 59 of, for example, 5V through a pull-up resistance 58 and a separate input port of the controller. Moreover, the other pin 57b of the body-side member 55b is connected with a ground 60. On the other hand, two pins 56a, 56b of the deck-side member 55a corresponding to pins 57a, 57b are connected with each other through a short circuit line 61. With this construction, a ground voltage, in short 0V, is input to the controller through the pin 57a under the condition that the paper supplying deck 50 is mounted on the paper supplying portion of the body 51, while a power source voltage, in short 5V, is input to the controller under the condition that the paper supplying deck 50 is not mounted on the body 51. It is confirmed on the side of the body 51 from this difference in input voltage whether or not the paper supplying deck 50 is mounted, and the paper supplying operation is started after confirming that the paper supplying deck 50 is mounted.
However, with the above described construction, problems have occurred in that not only are three pins required, i.e. two pins for detecting whether or not the paper supplying deck 50 is mounted on the body 51 and one pin for detecting the paper width, as pins of the drawer-type connector 55, but also the input port for inputting a mounting detecting signal and the input port for inputting a paper width detecting signal are required also for the controller on the side of the body 51. Thus, the cost is increased.
Besides, as for the conventional image forming apparatus, it has been known that a paper supplying deck mounted so as to be inserted into and withdrawn from a paper supplying portion of a body is provided with a sensor for detecting a size of a paper carried thereon, and a paper supplying operation is conducted in correspondence to the size of paper detected by means of such sensor.
In such detection of the size of the paper, it is necessary to detect sizes in two directions, that is the direction of width and the longitudinal direction. For example, as for typical papers of centimeter measure, it is required that the size in the direction of width is discriminated among six paper types, that is B6, A5, B5R, B5 and A4. Also, as for typical papers of inch measure, it is required that the size in the direction of width is discriminated among three paper types, that is 5.5.times.8.5, 8.5.times.11R and 8.5.times.11. On the other hand, the size in the longitudinal direction of such typical papers is absolutely determined in many cases depending upon the size in the direction of width.
That is to say, for example in case of the typical papers of centimeter measure, as shown in FIG. 11, the discrimination of B4 paper from B5 paper and of A4 paper from A3 paper can be conducted by confirming "Yes" or "No" on a rear portion of the paper by means of the sensor arranged at an appointed position in the longitudinal direction. This is equally true also in case of the typical papers of inch measure.
In the detection of the size in the direction of width of the paper in this case, a lead switch, a photo-interrupter, a slide-type variable resistor or the like can be used as the sensor, while in the detection of the size in the longitudinal direction, a lead switch, a photo-interrupter or the like can be used as the sensor.
However, in case of the conventional example, two detecting systems in the direction of width and the longitudinal direction have been required for discriminating the size of paper. For example, in an example where sensors corresponding to the respective sizes in the direction of width are provided, in the controller receiving size detecting signals from such sensors, in case of the typical papers of centimeter measure, the input port for receiving six types of size detecting signals in the direction of width and the input port for receiving one size detecting signal in the longitudinal direction have been required. That is to say, seven total input ports have been required in such case.
On the contrary, in the case where an output voltage V.sub.o changing depending upon a change of variable resistor 70, which is interlocked with a paper width setting mechanism, in resistance value is put in an analog input port of a controller 71 as the size detecting signal in the direction of width, as shown in FIG. 12, it is enough to use two input ports, that is the analog input port of the detecting signal in the direction of width and an input port of the detecting signal in the longitudinal direction detected by means of a switch 72.
However, also in this case, at least two systems of input ports have been required for discriminating the sizes of the respective typical papers by means of controller 71, and thus a problem has occurred in that a program for discriminating the sizes of papers in the controller 71 is complicated.